Timed-out trying to acquire PJSUA mutex

[Norman@xxxxxxxxx (Norman Franke)]

Any idea what can cause this? It dies in pjsip_inv_answer called by  
pjsua_call_answer while sending a code 180.

14:09:35.234   pjsua_call.c Timed-out trying to acquire PJSUA mutex  
(possibly system has deadlocked) in pjsua_call_get_conf_port()
../src/pjsip-ua/sip_inv.c:1666: failed assertion `inv->invite_tsx'
Program received signal:  "SIGABRT".

Norman Franke
ASD, Inc.